Nutrisse Hair Colour did not work

I have very long hair and have successfully been using Garnier Nutrisse Creme 6.23 - Rose Gold since January 2015. As the colour had faded quite a lot and I have some regrowth, I decided that for summer I would try a lighter shade Garnier Nutrisse Creme Hair Colour 7 Dark Blonde. The instructions recommended that I used a pre-lightener first and I bought 2 boxes of Garnier Nutrisse Truly Blonde Camomile 100 Very Light Blonde. After following the instructions carefully step by step for the recommended time, I was expecting to be blonde or considerably lighter as the box indicated that this colour lightens up to 4.5 tones and was recommended for dark brown to light brown hair. However, I was deeply disappointed to discover that there was very little difference to my hair colour. I had to buy 2 additional boxes to re-do the process but sadly after the desired time, the only thing lighter, are my roots. I am deeply disappointed, not only in the R600.00 and time wasted but especially since I now have to walk around with almost bleached roots and dark ends. Not attractive.Carlton Hair quoted me R1100.00 for a colour correction. I cannot afford this! PLEASE HELP